Geological grouting is a versatile construction technique used in a variety of applications. Injection casing or piping is driven into the ground. Grout is then pumped under pressure through the above-ground end of the installed casing, out the underground end, and into the surrounding soil. The grout itself can be made from many different materials proportioned in a wide range of amounts depending on the specific grouting application. Cementitious grout, for example, is a mixture of hydraulic cement and water, with or without aggregates and with or without admixtures. Hydraulic cements react with water to form a hardened paste that maintains its strength and durability in water and also maintains its properties upon drying.
Grouting applications include slabjacking, mud jacking, subsealing and soil grouting. In slabjacking, pressure grouting is used to raise a depressed section of pavement or other concrete element by forcing a flowable grout under it. Subsealing is where a cement-grout mixture is pumped under pressure through a packer installed in an access hole drilled in a slab to fill voids and depressions under the slab and reduce damage caused by excessive pavement deflections. For soil densification, soil is grouted to increase its bearing capacity, provide radial densification, reduce or halt settlement, increase shear resistance to stabilize it against lateral movement, reduce waterflow, or increase the cohesive strength of friable ground prior to excavation. Soil grouting includes permeation grouting, where a thin grout is used to permeate the soil and fill pores and voids between soil particles; deep-soil mixing, where soil and injected grout are mixed together to make a soil-cement material in place; jet grouting, where a cement-and-water grout is injected under very high pressure to form a concrete-like column; and compaction grouting, described below.
Compaction grouting is a soil stabilization process where weak or compromised sub-soils are densified. This technique involves driving injection casing into the soil in five to eight foot sections until good refusal is achieved, usually when the casing reaches bedrock or bearing strata. Pressure grouting is then performed in vertical stages throughout the length of the casing hole. The vertical stages are created by extracting a section of casing a fixed length, typically one to three feet, and then pumping a quantity of stiff, sand-and-cement grout through the casings. An operator monitors an external pump stroke counter at the pump and a pressure gauge at a pump head attached to the casing end. The operator also records the pressures achieved and the quantity of grout injected at each stage. A fully extracted section of casing is removed between stages, the pump head is reattached, and the extraction and grouting sequence is repeated. The stiff grout does not permeate the soil but maintains a grouted mass, three feet or more in diameter. By displacing the soil and forming a bulblike or coluninlike form, the grout significantly increases the soil density at a radial distance of one to six feet or more from the soil-grout interface.
Typically, injection casings for compaction grouting applications are installed with a handheld pneumatic or hydraulic hammer. One end of a casing section is attached to the end of a previously installed casing section. A crewman then stands atop a platform, positions the hammer to the unattached end of the casing, activates the hammer and drives the entire casing assembly into the ground. These steps are repeated multiple times.
Such handheld hammering methods, however, are potentially hazardous, awkward and time consuming. The pneumatic and hydraulic hammers are heavy and difficult to lift and position on the unattached casing end, which may extend five feet or more above ground-level. The crewman holding the heavy hammer is always at risk of falling off of the platform. This operation requires a two-man crew, with one man repeatedly climbing onto and off-of the platform and the other man transferring the hammer to and from the man on the platform and assisting in assembling the casing sections.
One aspect of the portable injection-casing driver according to the present invention is a driver tool for hammering a shaft into a surrounding media comprising a base plate and a tower attached to and extending generally perpendicularly from the base plate. The tower has a first end away from the base plate and a second end near the base plate. A powered hammer is movable along the tower between the first and second ends so that the shaft can be positioned between the media and the hammer when the hammer is near the first end of the tower and so that the shaft can be driven by the hammer into the media as the hammer is actuated and moved toward the second end.
The driver tool may also comprise a motor and a mount retained by the tower so as to be movable along the tower. The hammer is attached to the mount and a link is installed between the tower first and second ends. The link is utilized to transfer mechanical energy from the motor to the mount so as to move the hammer. The link may comprise an upper sprocket near the first end, a lower sprocket near the second end, a reduction gear and a drive chain engaging the sprockets and the gear. The motor also engages the gear. In one embodiment, at least one of the sprockets has a spring-loaded tension adjuster configured to dampen mechanical force generated during operation of the hammer. In another embodiment, the reduction gear has a gear ratio in the range of 50:1 to 70:1. In a further embodiment, the base plate has an open-faced slot configured to accommodate the shaft and balance and stabilize the tool. In another embodiment, the tower has a height in the range of 94 inches to 116 inches.
In yet another embodiment, the driver tool further comprises a control assembly having a first portion to direct power to the motor in order to raise and lower the hammer, and a second portion to direct power to the hammer in order to actuate and de-actuate the hammer. The first portion and the second portion are independently operable and configured to allow an operator to simultaneously lower and actuate the hammer with one hand. The motor and the hammer may be powered by compressed air. In this embodiment, the first portion comprises a dual-port valve controlled by a first handle to direct compressed air through the motor. The second portion comprises a single-port value controlled by a second handle to direct compressed air to the hammer.
In still another embodiment, the driver tool further comprises a wheel assembly. The tool is movable between an operating position having the base plate positioned against the media and a transport position having the wheel assembly positioned against the media so as to provide manual portability for the tool. The wheel assembly may be offset from the media in the operating position so as to increase stability for the tool. The base plate may be offset from the media in the transport position so as to increase portability of the tool. The driver tool may also have a brace that is deployed in the operating position to enhance the stability of the tool. The brace is folded against the tool in the transport position to enhance the portability of the tool.
Another aspect of the present invention is a method of installing a shaft into a surrounding media comprising the steps of providing motorized movement of a powered hammer along a tower, stabilizing the tower generally perpendicularly to the media, positioning the shaft proximate the tower lengthwise between the hammer and the media, and driving the shaft with the hammer into the media. The stabilizing step may comprise the substeps of attaching the tower to a generally planar base plate so that the tower extends in a direction normal to the base plate, and placing a face of the base plate against the media. The positioning step may comprise the substeps of providing an open-faced slot in the base plate and locating the shaft within the slot. The driving step may comprise the substeps of raising the hammer along the tower and away from the media so as to enable a first end of the shaft to be positioned near the hammer and a second end of the shaft to be positioned against the media and positioning the hammer so as to contact the shaft with a bit installed in the hammer. Further substeps are actuating the hammer so as to repeatedly strike the shaft with the bit and lowering the hammer along the tower and toward the media during the actuating step so as to maintain contact between the bit and the shaft.
Yet another aspect of the present invention is a driver tool for installing a shaft into a media comprising a base means for supporting the tool and accommodating the shaft, a hammer means for repeatedly striking the shaft, and a tower means attached to the base means for movably retaining the hammer means. The driver tool may further comprise a motor and a positioning means actuated by the motor for moving the hammer means along the tower means. Also, the driver tool may comprise a control means for independently routing power to the hammer means and the motor. The driver tool may further comprise a transport means for manually moving the tool.
The driver tool of the present invention has many advantages over present methods of installing injection casings and other shaft media into the ground. Because the hammer is slidably mounted to a tower, it eliminates the need of an operator handling this heavy piece of equipment. The tower allows the hammer to be precisely positioned on a casing end several feet above ground-level, eliminating the need for an operator to stand on a platform, with the associated safety risks. Unlike heavy equipment used for driving shafts into the ground, the driver tool is compact for operation in limited access areas and can utilize relatively small shaft sections compared with heavy equipment. The mounted turf tires and the size and balance of the driver tool allow portability by one or two men.